1. Field of the Invention
The present invention relates to an attachment structure to a circuit board, for example, for attaching an electronic component such as an instrument movement or the like to a rigid circuit board, and a clip used in the attachment. Particularly, the present invention relates to an attachment structure of an electronic component to a circuit board, by which the workability and economy in attachment of an attachment member to a rigid circuit board can be enhanced, and a clip for use in the attachment.
2. Description of the Related Art
For example, a conventional structure with which an instrument movement (electronic component) for use in assembling an on-vehicle instrument apparatus is attached to a rigid circuit board of the on-vehicle instrument apparatus will be described with reference to FIG. 10. The reference numeral 1 represents a rigid circuit board. A predetermined printed pattern circuit 2 is formed in the lower surface of the rigid circuit board 1.
The reference numeral 3 represents an instrument movement such as a speedometer, an engine tachometer, or the like, attached to the upper surface of the rigid circuit board 1. Although the instrument movement 3 does not have a feature in internal configuration, the schematic configuration thereof will be described as follows. The reference numeral 4 represents a housing made of resin. The housing 4 also has a function as a coil bobbin. Inside the housing 4, a movable magnet 5 is rotatably supported through a pointer shaft 6. In addition, a pair of coils are wound and retained around the housing 4 perpendicularly to each other so as to form a cross coil 7.
The reference numeral 8 represents a shield case disposed to cover the outside of the cross coil 7; 9, connection terminals connected to the cross coil 7; and 10, a pointer attached to a forward end of the pointer shaft 6.
When the instrument movement 3 configured thus is attached to the rigid circuit board 1, the instrument movement 3 is put on the upper surface of the rigid circuit board 1. Further, attachment holes 11 provided in the rigid circuit board 1 are made to agree with threaded holes 12 formed in the housing 4 of the instrument movement 3. Then, attachment screws 13 are made to pass through the attachment holes 11 from the lower surface (back side) of the rigid circuit board 1. The attachment screws 13 are screwed down into the threaded holes 12 of the instrument movement 3 so that the rigid circuit board 1 and the instrument movement 3 are screwed to each other.
In such a manner, in the attachment structure in which the rigid circuit board 1 and the instrument movement 3 are screwed to each other by the attachment screws 13, a plurality of attachment screws 13 for screwing must be prepared in advance, and a screwing step for screwing the plurality of attachment screws is required. From such a point, the attachment structure is inferior in the workability and economy in attachment of the instrument movement.
In addition, after the instrument movement 3 is screwed to the rigid circuit board 1, the lower surface of the rigid circuit board 1 is immersed in a flow soldering tank so that the connection terminals 9 projecting from the lower surface of the rigid circuit board 1 are soldered with the printed circuit 2. At this time, however, there arises a problem that solder balls repelled by the head portions of the attachment screws 13 adhere to a circuit portion of the rigid circuit board so as to cause an electric connection failure (short-circuit due to a solder bridge or the like).
As mentioned above, when the head of each attachment screw is immersed into the flow soldering tank, the head thereof might repel the solder to form the solder balls. On occasion, the solder balls are attached to another soldering potion which might arise a loose connection in the circuit board 1. In order to avoid the loose connection, in the conventional art, the IC, the resistor and the like except for the instrument movement 3 are flow-soldered in the flow soldering bath to electrically fix them to the circuit board 1. After that, the instrument movement 3 is screwed and fixed to the circuit board 1, and then the terminals of the instrument movement 3 are spot-soldered with the wiring pattern of the circuit board 1 so that the instrument movement 3 is fixed and electrically connected with the circuit board 1. Therefore, the soldering of the instrument movement 3 and the soldering of other electronic components, such as an IC, a resistor and the like, have to be performed in separate steps, respectively. Two soldering steps are required in total.
To solve such a problem, it can be considered to give surface treatment to the head portions of the attachment screws 13 so as to make solder easy to adhere to the head portions. However, it is not practical because the treatment cost increases when surface treatment is given to the respective head portions of the attachment screws 13 so as to make solder easy to adhere to the head portions.
On the other hand, if the soldering is carried out by a robot without using the flow soldering tank as means for soldering the connection terminals 9 with the circuit portion of the rigid circuit board, it is possible to restrain generation of solder balls on the head portions of the attachment screws 13. However, in such robot soldering means, it is necessary to solder respective portions to be soldered one by one. Therefore, it takes much time for soldering so that the assembling productivity deteriorates.
Alternately, there has been proposed to provide a resin engagement nail integrally formed with a resin bobbin with which a coil is wound. In the attachment process, the resin engagement nail is fixed to the circuit board 1. However, since the engagement nail is made of resin, the resin engagement nail deforms due to the heat generated in the flow soldering. To avoid the deformation of the resin engagement nail, only the IC, the resistor and the like are flow-soldered in the flow soldering bath to electrically fix them to the circuit board 1. After that, the instrument movement 3 is fixed to the circuit board 1 through the resin engagement nail, and then the terminals of the instrument movement 3 are spot soldered with the printing pattern of the circuit board 1 so that the instrument movement 3 is fixed and electrically connected with the circuit board 1 without deformation of the resin engagement nail. In this method, the two soldering steps are also required in total.
To improve the attaching efficiency of the instrument movement 3, it is possible to use a bobbin a resin engagement nail made of high heat resistance resin. However, the high heat resistance resin is expensive in general, which increases the manufacturing cost thereof, and therefore it is not practical.
The present invention is made in consideration of such facts in the conventional. It is an object of the present invention to enable an electronic component such as an instrument movement or the like to be fixed to a rigid circuit board simply and easily without using any attachment screw when the electronic component is attached to the rigid circuit board, so that the number of man-hours for fastening attachment screws is omitted.
It is also an object of the present invention to carry out the soldering work for a connection circuit in the lower surface (back surface) of the rigid circuit board by use of a flow soldering tank so that the workability and economy of the soldering are enhanced.
To attain the foregoing first and second objects, according to an aspect of the present invention, there is provided an attachment structure of an electronic component to a circuit board comprising: a rigid circuit board having a suitable circuit pattern formed on a back surface thereof, having one or more attachment holes formed in the rigid circuit board for attachment of an electronic component, and further having soldering lands provided at circumferential edges of the attachment holes on the back surface of the rigid circuit board; an electronic component having one or more clip pass-through holes formed in positions in which the clip pass-through holes are coincident with the attachment holes correspondingly on a front surface of the rigid circuit board; and solderable clips for passing through the clip pass-through holes and the attachment holes correspondingly to perform fixed positioning of the electronic component to the rigid circuit board, each of the clips having an engagement portion portion at one end thereof and a pair of elastic engagement portions at the other end thereof, the engagement portion portion being engaged with a clip entrance side hole edge of corresponding one of the clip pass-through holes formed in the electronic component, the elastic engagement portions being engaged with a land formation surface side hole edge of corresponding one of the attachment holes provided in the rigid circuit board so that the elastic engagement portions can be displaced elastically in a direction of a hole diameter of the attachment hole; wherein, at the time when the rigid circuit board and the electronic component are fixedly positioned by the clips, the engagement portion portions of the clips are engaged with the electronic component, and forward end portions of the elastic engagement portions are soldered with the lands formed on the rigid circuit board.
Thus, according to this attachment structure, the attachment of the electronic component to the rigid circuit board can be ensured by the engagement force of the clips and the soldering between the clips and the lands provided on the rigid circuit board. As a result, the workability in attaching the electronic component to the rigid circuit board is improved on a large scale.
According to another aspect of the present invention, a clip for fixing the electronic component to the rigid circuit board is characterized by comprising: a solderable and flexible/elastic metal piece which is bent into an V-shape along a longitudinal direction thereof and along a center thereof so as to form a bent piece; a pair of flexible/elastic pieces formed by forming a notch slit along a ridge line formed by bending the metal piece into the pair of bent pieces in the longitudinal direction and from a middle of the ridge line toward a forward end of the metal piece; engagement protrusions formed in vicinities of forward end portions of the flexible/elastic pieces, the engagement protrusions being inserted into and engaged with attachment holes formed in a rigid circuit board, respectively; and engagement portion formed at edges of the bent piece parallel to a ridge line of the bent piece and opposite to the flexible/elastic pieces of the bent piece, the engagement portion being pressed into and engaged with a clip pass-through hole formed in an electronic component.
Thus, by using such a clip to fix an electronic component to a rigid circuit board, the rigid circuit board and the electronic component can be fixedly positioned by one touch. In addition, by fixing the clip to the rigid circuit board by soldering, it is possible to ensure the connection among the clip, the electronic component, and the circuit board. Thus, the workability in attachment of the electronic component to the rigid circuit board becomes excellent.